Make av1/encoder/allintra_vis.h safe for C++

A follow-up to commit 46bd978.

Bug: b/558417547
Bug: b/558463892
Bug: b/558516408
Bug: b/558589747
TAG=wtc

Change-Id: Ic91a4f7c8569c0042ce4faae46774e2b1e278329

av1/encoder/allintra_vis.h

diff --git a/av1/encoder/allintra_vis.h b/av1/encoder/allintra_vis.h
index ee0b691..492defa 100644
--- a/av1/encoder/allintra_vis.h
+++ b/av1/encoder/allintra_vis.h
@@ -20,6 +20,10 @@
 #include "av1/encoder/block.h"
 #include "av1/encoder/encoder.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #define MB_WIENER_MT_UNIT_SIZE BLOCK_64X64
 
 void av1_init_mb_wiener_var_buffer(AV1_COMP *cpi);
@@ -48,4 +52,8 @@
 int av1_get_sbq_variance_boost(const AV1_COMP *const cpi, const MACROBLOCK *x);
 #endif
 
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
 #endif  // AOM_AV1_ENCODER_ALLINTRA_VIS_H_

test/encode_api_test.cc

diff --git a/test/encode_api_test.cc b/test/encode_api_test.cc
index 68eaaf4..5621933 100644
--- a/test/encode_api_test.cc
+++ b/test/encode_api_test.cc
@@ -31,9 +31,7 @@
 
 #include "av1/common/blockd.h"
 #include "av1/common/reconintra.h"
-extern "C" {
 #include "av1/encoder/allintra_vis.h"
-}
 #include "test/codec_factory.h"
 #include "test/encode_test_driver.h"
 #include "test/util.h"